Background: The parasitic protozoan Toxoplasma gondii is the cause of serious diseases known as toxoplasmosis. All warm-blooded vertebrate animals are susceptible to infection. Despite its significance, recent data on the prevalence and genetic diversity of T. gondii in human and sheep populations in central Iraq are limited.
Objectives: This study aimed to determine the prevalence of T. gondii infection in humans and sheep in Diyala and Baghdad provinces, Iraq, using serological and molecular techniques, and to genetically characterize circulating strains based on the regenerating gene (Reg).
Methods: The one hundred placentas of sheep in Diyala and Baghdad (50 samples from each province) were examined. An infected sheep placenta sample was digested with the pepsin enzyme. This was intended for performing the dyeing process with Giemsa stain and extracting the genomic DNA, using the tissue genomic DNA isolation kit (buffy coat) of seropositive individuals with Geneaid, Bioteccorp, Taiwan. Polymerase chain reaction (PCR) amplification targeted a 529 bp fragment of the REGs gene in T. gondii. Human serum samples were collected from 100 human blood samples (male and female) from Diyala and Baghdad (50/50). The enzyme-linked immunosorbent assay (ELISA) results were recorded according to the manufacturer’s instructions. The study period was from September 2024 to April 2025.
Results: The overall infection rate in sheep was 25% (25/100), with a higher rate in Diyala (30.3%) than in Baghdad (20%). In ewes, the highest prevalence (43.33%) was observed at 4 years of age. ELISA testing of human sera (n=100) revealed an overall seroprevalence of 23.91%. The rate was significantly higher in Diyala (30.95%) than in Baghdad (18%), and higher in females (40%) than in males (4.76%). The highest infection rate (33.33%) was found in the 25-35-year age group. “Phylogenetic analysis of the Reg sequences showed that Iraqi isolates clustered most closely with strains from Iraq, Indonesia, China, Italy, Netherlands, Pakistan, Turkey, Iran, Chile, Myanmar, Nigeria, Saudi Arabia, and India. Phylogenetic analysis of the evolutionary distribution of REGs in 20 local isolates detected in Diyala and Baghdad (the middle of Iraq), with 36 global isolates of T. gondii deposited in GenBank, indicated a diverse evolutionary lineage.
Conclusion: This study confirms that toxoplasmosis remains a highly endemic zoonosis in central Iraq, with a significant prevalence in both sheep and human populations. The high genetic diversity of T. gondii strains and the identified risk factors (location, gender, and age) highlight the need for targeted public health and veterinary control measures.